In the pharmacy, colds and flu are commonly treated illnesses, and medicines that contain decongestants, antihistamines, analgesics, cough suppressants and expectorants are used alone, or in combination, to relieve typical symptoms. Combination cold and flu medicines can have certain adverse effects on the autonomic nervous system. This article provides an overview of the functioning of the autonomic nervous system (ANS), the pharmacological effects of the common ingredients in cold and flu medicines on the ANS, as well as the contraindications to consider when offering these medicines.